Passive rf devices that communicate using a wireless network protocol

ABSTRACT

Passive RF devices are disclosed that communicate using a wireless network protocol. The device includes an antenna operable to receive a radio frequency (RF) signal from a RF source that transmits the RF signal based on a wireless network protocol. The device further includes circuitry operable to derive power from the RF signal. With the power derived from the RF signal, the circuitry is further operable to read data from a memory, to encode the data based on the wireless network protocol, and to modulate the RF signal to include the encoded data. The antenna is further operable to transmit the modulated RF signal based on the wireless network protocol for reception by the RF source or another passive RF device.

RELATED APPLICATIONS

This non-provisional application is a divisional of U.S. patentapplication Ser. No. 13/216,810, filed on Aug. 24, 2011 and titled“PASSIVE RF DEVICES THAT COMMUNICATE USING A WIRELESS NETWORK PROTOCOL,”which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to the field of passive Radio Frequency (RF)devices.

BACKGROUND

Radio Frequency Identification (RFID) refers to a process oftransferring data over a Radio Frequency (RF) signal between a readerand a device that is attached to an object. RFID is commonly used foridentifying and tracking objects. For example, RFID devices may beattached to objects in a warehouse so that inventory in the warehousemay be tracked. The RFID device, also referred to as an RFID tag,typically stores an identifier (ID) for an object in a memory. The RFIDdevice reads the object ID from the memory, and broadcasts an RF signalthat includes the object ID (e.g., the object ID is modulated on the RFsignal). An RFID reader receives the RF signal and interprets the objectID from the RF signal.

Most RFID devices include an antenna that receives and transmits RFsignals, and an integrated circuit that stores data and processes the RFsignals. Some RFID devices also include a battery, and are referred toas active devices. Other RFID devices do not include a battery, and arereferred to as passive devices. In a passive RFID device, the power forthe integrated circuit is supplied by an RF signal supplied by the RFIDreader. The antenna in the passive RFID device receives the RF signalbroadcast from the RFID reader. The antenna has a coiled configurationwhich causes the RF signal to form an electromagnetic field in theantenna. The integrated circuit derives power from the electromagneticfield, which energizes the integrated circuit instead of a battery orsome other power source. With the power supplied by the RF signal, theintegrated circuit reads the data stored in memory, and modulates thestored data onto the RF signal. The antenna then transmits or reflectsthe modulated RF signal for reception by the RFID reader. The RFIDreader senses the RF signal from the passive RFID device, and processesthe data added to the RF signal.

SUMMARY

Embodiments described herein provide for an improved passive RF devicethat is able to communicate using a wireless network protocol. Thepassive RF device includes circuitry that is able to derive power froman RF signal that is transmitted from a RF source. The RF signals fromthe RF source are based on the wireless network protocol (e.g., IEEE802.15.4 or IEEE 802.11). With the power derived from the RF signal, thecircuitry is able to communicate with the RF source or other passive RFdevices using the wireless network protocol. Thus, passive RF devices,such as RFID devices, may be implemented in a more effective andreliable manner by using the wireless network protocol forcommunication.

One embodiment includes a passive RF device. The device includes anantenna operable to receive a radio frequency (RF) signal from a RFsource that transmits the RF signal based on a wireless networkprotocol. The device further includes circuitry operable to derive powerfrom the RF signal. With the power derived from the RF signal, thecircuitry is further operable to read data from a memory, to encode thedata based on the wireless network protocol, and to modulate the RFsignal to include the encoded data. The antenna is further operable totransmit the modulated RF signal based on the wireless network protocolfor reception by the RF source or another passive RF device.

Other exemplary embodiments may be described below.

DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are now described, by way ofexample only, and with reference to the accompanying drawings. The samereference number represents the same element or the same type of elementon all drawings.

FIG. 1 is a block diagram illustrating an RFID system in an exemplaryembodiment.

FIG. 2 is a block diagram of a passive RF device in an exemplaryembodiment.

FIG. 3 is a flow chart illustrating a method of operating a passive RFdevice to communicate using the wireless network protocol in anexemplary embodiment.

FIG. 4 illustrates a frame in an exemplary embodiment.

FIG. 5 illustrates an application of passive RF devices to monitor thepower usage of an electrical device in an exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

The figures and the following description illustrate specific exemplaryembodiments of the invention. It will thus be appreciated that thoseskilled in the art will be able to devise various arrangements that,although not explicitly described or shown herein, embody the principlesof the invention and are included within the scope of the invention.Furthermore, any examples described herein are intended to aid inunderstanding the principles of the invention, and are to be construedas being without limitation to such specifically recited examples andconditions. As a result, the invention is not limited to the specificembodiments or examples described below, but by the claims and theirequivalents.

FIG. 1 is a block diagram illustrating an RFID system 100 in anexemplary embodiment. RFID system 100 includes an RF source 102 andpassive RF devices 104-105. RF source 102 is an active device thattransmits RF signals based on a wireless network protocol. A wirelessnetwork protocol defines a format for data being transmitted, and rulesfor transmission of the data. Examples of a wireless network protocolthat may be used in RFID system 100 are IEEE 802.15.4, Zigbee, IEEE802.11, Wi-Fi, etc. RF source 102 may include an RFID reader that iscompliant with the wireless network protocol, or may include a wirelessaccess point for a Personal Area Network (PAN), a Local Area Network(LAN), or another type of network that uses the wireless networkprotocol.

RF devices 104-105 are passive devices, meaning that they derive powerfrom RF signals received from RF source 102 instead of from an activepower source, such as a battery. Each RF device 104-105 is programmedwith data, such as an identifier (ID) for an object. Using the powerderived from the RF signal, an RF device 104 identifies its stored data,and encodes the data based on the wireless network protocol. RF device104 then transmits the encoded data based on the wireless networkprotocol. The encoded data may be sent to RF source 102 or to anotherpassive RF device (e.g., RF device 105).

FIG. 2 is a block diagram of passive RF device 104 in an exemplaryembodiment. RF device 104 includes an antenna 202 and circuitry 204.Antenna 202 is operable to transmit and receive RF signals based on thewireless network protocol. Circuitry 204 includes a power circuit 206, amemory 208, and a processor 210. Power circuit 206 is operable to derivepower from a RF signal received from RF source 102 through antenna 202.The power derived from power circuit 206 energizes circuitry 204 insteadof a battery or some other active power source, which makes RF device104 a passive device. Memory 208 is operable to store data, such as anidentifier (ID) for an object. Memory 208 may store other programs orcommands executable by processor 210, or any other desired data.Processor 210 is programmable to provide the desired functionality of RFdevice 104. One of the functions provided by processor 210 is to reportthe data that is stored in memory 208. Another one of the functionsprovided by processor 210 is to communicate with RF source 102 and/or RFdevice 105 using the wireless network protocol.

The protocol-based communication for RF device 104 is provided by aprotocol element 212 within processor 210. Protocol element 212 as shownin FIG. 2 represents the function in RF device 104 for exchanging databased on the wireless network protocol (e.g., IEEE 802.15.4 or IEEE802.11). As part of exchanging data, protocol element 212 is able toencode data based on the wireless network protocol for transmission toRF source 102 and/or RF device 105. Protocol element 212 is also able todecode data received from RF source 102 and/or RF device 105 based onthe wireless network protocol.

Assume in FIG. 1 that RF source 102 transmits an RF signal based on thewireless network protocol while RF device 104 is in close proximity toRF source 102. FIG. 3 is a flow chart illustrating a method 300 ofoperating passive RF device 104 to communicate using the wirelessnetwork protocol in an exemplary embodiment. The steps of method 300will be described with respect to RF device 104 of FIGS. 1-2, althoughone skilled in the art will understand that the methods described hereinmay be performed by other devices not shown. The steps of the methodsdescribed herein are not all inclusive and may include other steps notshown. The steps for the flow charts shown herein may also be performedin an alternative order.

In step 302, antenna 202 receives the RF signal from RF source 102.Again, the RF signal from the RF source 102 is based on the wirelessnetwork protocol. In step 304, power circuit 206 derives power from theRF signal. For example, antenna 202 may have a coiled configurationwhich causes the RF signal to form an electromagnetic field in antenna202. Power circuit 206 may then derive the power from theelectromagnetic field, which energizes circuitry 204.

With the power derived from the RF signal, processor 210 reads the datathat is stored in memory 208 in step 306. Instead of simply modulatingthe data on the RF signal and transmitting the modulated RF signal,protocol element 212 encodes the data based on the wireless networkprotocol in step 308. The wireless network protocol defines how the datais structured or formatted for transmission into a data unit. Forexample, the wireless network protocol may define the structure of thedata unit as including a header and an attached payload. The header mayinclude fields for addressing, such as a source address and adestination address. The header may also include a field indicating a“type” for the data unit. For instance, if IEEE 802.15.4 is used as thewireless network protocol, then the type of data unit may be for data,an acknowledgement, a beacon, or a Media Access Control (MAC) command.If IEEE 802.11 is used as the wireless network protocol, then the typeof data unit may be a User Datagram Protocol (UDP) packet orTransmission Control Protocol (TCP) packet.

One type of data unit used for lower-level networking protocols is aframe. One example of a frame is shown in FIG. 4. Frame 400 in FIG. 4includes a header 410 that includes control and/or addressinginformation. In this embodiment, header 410 includes a preamble field412, a destination address field 414, a source address field 416, and aframe type field 418. The destination address field 414 and sourceaddress field 416 may include MAC addresses for the destination andsource of the frame 400, respectively. Frame 400 further includes apayload 420, which includes the actual data that is being transported,such as an object ID. Frame 400 also includes a frame check sequence 430that is used for error checking. The structure of frame 400 in FIG. 4 isjust one example, as the frames or other data units discussed herein mayhave other desired structures.

If IEEE 802.11 is used as the wireless network protocol, one type ofdata used for lower level networking is the Service Set Identifier(SSID). The SSID is a name that identifies a particular 802.11 wirelessLAN and is defined as 2 to 32 8-bit bytes. The SSID is typicallybroadcast as an identifier by 802.11 servers so that clients can choosewhether they should connect to that server. RF device 104 may encode thedata in an SSID, and then modulate and transmit that data so that it'sreceived by RF source 102 and passive RF device 105. The SSID mayinclude an identifier for the device and the content of memory 208. Forexample, the identifier may be 3 bytes and the memory content may be 29bytes. Or, the identifier may be 0 bytes and the entire 32 bytes may beused for the memory content. Or, the initial N bytes of the SSID may beallocated for a sequence number (e.g., 0,1,2,3 for 4-bytes sequence ofSSID's), N bytes for the maximum sequence number, and the subsequent32-2N bytes for the memory content. Processor 210 may encode the contentof memory 208 in successive SSID's in increasing order of sequencenumber, and repeatedly broadcast that sequence of SSID's. The receiverthen reassembles the data encoded in the SSID's. For example, whentransmitting a 75 byte message, three SSID's would be used and theirbyte patterns would look like: 02[30 byte payload], 12[30 byte payload],22[15 bytes of payload data out of 30 that are available].

After the data is encoded in FIG. 3, processor 210 modulates the RFsignal to include the encoded data in step 310. Antenna 202 thentransmits the modulated RF signal based on the wireless network protocolin step 312. Antenna 202 may be able to actively transmit the modulatedRF signal based on power derived from power circuit 206. Antenna 202 mayalternatively reflect or backscatter the RF signal that is received fromRF source 102 after it is modulated. Either way, the modulated RF signalis transmitted for reception by RF source 102 and/or RF device 105.

If the data is intended for RF source 102, then protocol element 212 mayencode the data with an address (e.g., a MAC address) for RF source 102.When RF source 102 receives the modulated RF signal, RF source 102extracts the encoded data from the modulated RF signal, and decodes thedata. RF source 102 may process the decoded data to identify thedestination address. If the destination address in the data matches theMAC address for RF source 102, then RF source 102 determines that it isthe intended recipient for the data. RF source 102 may then handle thedata in a desired manner.

If the data is intended for another passive RF device, such as RF device105, then protocol element 212 may encode the data with an address(e.g., a MAC address) for RF device 105. The modulated RF signal fromantenna 202 is then received in RF device 105, which processes themodulated RF signal similar to the way RF source 102 processes the RFsignal as described above.

The use of the wireless network protocol in RFID system 100 allows forbi-directional communication between RF device 104 and RF source 102.For example, the wireless network protocol may specify request-responseprocedures for transmission of data or commands. One of therequest-response procedures may be for RF source 102 to request the datafrom RF device 104. Therefore, before RF device 104 sends the encodeddata to RF source 102, RF source 102 may request the data from RF device104 based on the wireless network protocol. To do so, RF source 102generates a request for the data stored on RF device 104, and encodesthe request based on the wireless network protocol. The request may befor all data stored in RF device 104, or may indicate specific databeing requested (e.g., by file name). RF source 102 then modulates theRF signal to include the encoded request. Antenna 202 in RF device 104receives the RF signal from RF source 102, and circuitry 204 decodes theencoded request from the RF signal based on the wireless networkprotocol. In response to the request from RF source 102, circuitry 204reads the requested data from memory 208, encodes the data based on thewireless network protocol, and modulates the RF signal to include theencoded data as described in FIG. 3 to provide the data to RF source102.

Another one of the request-response procedures may be for RF source 102to acknowledge receipt of the data from RF device 104. When RF source102 successfully receives the data from RF device 104, RF source 102generates an acknowledgement, and encodes the acknowledgement based onthe wireless network protocol. RF source 102 then modulates the RFsignal to include the encoded acknowledgement. Antenna 202 in RF device104 receives the RF signal from RF source 102, and circuitry 204 decodesthe encoded acknowledgement based on the wireless network protocol.Circuitry 204 may then process the acknowledgement from RF source 102 todetermine that the data was successfully received in RF source 102. Ifthe data was not successfully received, then circuitry 204 may retrytransmission of the data.

Another one of the request-response procedures may be for RF device 104to request that RF source 102 sustain the RF signal for a time period.Because RF device 104 is a passive device, it relies on the RF signalfor power. If processor 210 in RF device 104 is tasked with performing afunction, then it is preferred that the RF signal is available to powerprocessor 210 for the duration of the task. Thus, processor 210 mayrequest that RF source 102 sustain the RF signal for the duration of thetask. To do so, circuitry 204 encodes a request to sustain the RF signalfor a time period (e.g., the time period required to complete thefunction) based on the wireless network protocol. Circuitry 204 thenmodulates the RF signal to include the encoded request for transmissionto RF source 102 through antenna 202. When RF source 102 receives themodulated RF signal, RF source 102 extracts the encoded request from themodulated RF signal, and decodes the request. RF source 102 determinesthat RF device 104 has requested that the RF signal be supplied for atime period, and maintains the RF signal for the requested time periodso that RF device 104 may complete a task.

The request-response procedures in the wireless network protocol mayallow for additional features in RFID system 100. For instance, RFsource 102 may request particular data from RF device 104, may requestwhen RF device 104 transmits the data, may request how often RF device104 transmits the data, etc. RF device 104 may make similar requests toRF source 102.

The use of the wireless network protocol in RFID system 100 also allowsfor bi-directional communication between RF device 104 and other passiveRF devices (e.g., RF device 105). Using the request-response proceduresin the wireless network protocol, RF device 104 may request data from RFdevice 105, and vice-versa. For example, assume that RF device 105requests data that is stored in RF device 104. To do so, RF device 105generates a request for the data stored on RF device 104, and encodesthe request based on the wireless network protocol. As with RF device104, RF device 105 is powered from the RF signal provided by RF source102. RF device 105 modulates the RF signal to include the encodedrequest, and transmits the modulated RF signal. Antenna 202 in RF device104 receives the RF signal from RF device 105, and circuitry 204 decodesthe encoded request based on the wireless network protocol. In responseto the request from RF device 105, circuitry 204 reads the data frommemory 208, encodes the data based on the wireless network protocol, andmodulates the RF signal to include the encoded data as described in FIG.3. Antenna 202 then transmits the modulated RF signal for reception byRF device 105. RF device 105 may then decode the data from the RFsignal.

The use of a wireless network protocol in RFID system 100 (see FIG. 1)advantageously allows for improved communication between RF source 102and RF devices 104-105. The wireless network protocol (through the RFsignals) both powers RF devices 104-105, and allows for bi-directionalcommunication (e.g., request-response procedures) between RF source 102and RF devices 104-105. The data transmission is more secure and morereliable using the wireless network protocol. Also, RF devices 104-105can communicate directly with access points or other protocol-compliantsources without the need for a dedicated RFID reader.

The passive RF devices described above may be used in a variety ofapplications. FIG. 5 illustrates an application of passive RF devices tomonitor the power usage of an electrical device 510 in an exemplaryembodiment. The electrical device 510 in FIG. 5 is illustrated as aprinter just as an example, as electrical device 510 may include acomputer, a television, a stove, a fan, or any other type of device thatuses electricity. A passive RF device 520 is attached to power cord 511of electrical device 510. The power cord 511 in turn is plugged into apower strip 530. Power strip 530 includes a passive RF device 521 and anactive RF device 525. Power strip 530 is a smart power outlet, as itincludes functionality for monitoring power usage of a device that isplugged into one of its outlets. One example of power strip 530 is aModlet that is manufactured by ThinkEco. Power strip 530 is plugged intowall outlet 540 that includes a passive RF device 522.

Passive RF device 520 of power cord 511 is programmed with an ID forelectrical device 510. The ID for electrical device 510 may include aserial number, a model number, and/or other information. Passive RFdevice 521 is programmed with an ID for power strip 530. The ID forpower strip 530 may include a serial number, a model number, and/orother information. Passive RF device 522 is programmed with an ID forwall outlet 540. The ID for wall outlet 540 may include a location(e.g., room number, floor number, etc), a model number, and/or otherinformation. This example will show how passive RF devices 520-522communicate their stored IDs using a wireless network protocol so thatthe power usage of electrical device 510 may be monitored.

When power strip 530 is plugged into wall outlet 540, and power cord 511is plugged into power strip 530, active RF device 525 is positioned veryclose (i.e., within inches) to each of the passive RF devices 520-522.Active RF device 525 acts as an RF source to transmit an RF signal basedon the wireless network protocol. Assume for this example that thewireless network protocol is IEEE 802.15.4, but other protocols may beused in other embodiments.

Passive RF device 520 on power cord 511 receives the RF signal fromactive RF device 525, and derives power from the 802.15.4 RF signal.Because passive RF device 520 is located close to active RF device 525,passive RF device 520 is able to derive enough power to support anetwork-based protocol such as 802.15.4. With the power derived from theRF signal, passive RF device 520 reads the ID for electrical device 510that is stored in memory, encodes the ID based on the 802.15.4 protocol,and modulates the RF signal to include the encoded ID. Passive RF device520 then transmits the modulated RF signal based on the 802.15.4protocol. The modulated RF signal is received in active RF device 525,which extracts and decodes the ID for electrical device 510 from the RFsignal.

Passive RF device 521 on power strip 530 works in a similar manner toprovide the ID for power strip 530. More particularly, passive RF device521 receives the RF signal from active RF device 525, and derives powerfrom the 802.15.4 RF signal. With the power derived from the RF signal,passive RF device 521 reads the ID for power strip 530 that is stored inmemory, encodes the ID based on the 802.15.4 protocol, and modulates theRF signal to include the encoded ID. Passive RF device 521 thentransmits the modulated RF signal based on the 802.15.4 protocol. Themodulated RF signal is received in active RF device 525, which extractsand decodes the ID for power strip 530 from the RF signal. Because powerstrip 530 is able to determine power usage through each of its outlets,active RF device 525 may also determine the power usage of electricaldevice 510 over a time period.

Passive RF device 522 on wall outlet 540 works in a similar manner topassive RF devices 520-521 to provide the ID for wall outlet 540 toactive RF device 525. Active RF device 525 then aggregates the ID forelectrical device 510, the ID for power strip 530, the ID for walloutlet 540, and the power usage information. Active RF device 525 thentransmits the aggregated information (e.g., an aggregated file) tocomputer 550 through a 802.15.4 access point 552. Computer 550 may thenexecute an application 551 that processes the IDs and the usageinformation to monitor the power load from electrical device 510.Application 551 may log how much power electrical device 510 draws overa time period to identify a peak power usage. Application 551 may loghow much power electrical device 510 draws for a particular function orprocessing event. For example, if electrical device 510 is a printer asin FIG. 5, then application 551 may log how much power the printer drawswhen printing a document and encode that in the transmitted data.

The power monitoring described above may be expanded to multipleelectrical devices and multiple wall outlets. Thus, a mesh network ofpassive RF devices may be formed to report IDs for each of theelectrical devices. This allows for large scale monitoring of powerusage, which is especially useful in large enterprises or campuses sothat power consumption may be regulated or reduced.

Although specific embodiments were described herein, the scope of theinvention is not limited to those specific embodiments. The scope of theinvention is defined by the following claims and any equivalentsthereof.

We claim:
 1. A Radio Frequency Identification (RFID) system comprising:an active Radio Frequency (RF) device operable to transmit an RF signalbased on a wireless network protocol; a first passive RF device attachedto a power cord of an electrical device, the first passive RF deviceoperable to store an identifier (ID) for the electrical device, toderive power from the RF signal, and to transmit the ID for theelectrical device to the active RF device based on the wireless networkprotocol; and a second passive RF device attached to a power strip thatreceives the power cord for the electrical device, the second passive RFdevice operable to store an ID for the power strip, to derive power fromthe RF signal, and to transmit the ID for the power strip to the activeRF device based on the wireless network protocol; the active RF deviceis further operable to retrieve power usage data for the electricaldevice from the power strip, and to aggregate the ID for the electricaldevice, the ID for the power strip, and the power usage data for theelectrical device.
 2. The RFID system of claim 1 further comprising: athird passive RF device attached to a wall outlet that electricallyconnects to the power strip, the third passive RF device operable tostore an ID for the wall outlet, to derive power from the RF signal, andto transmit the ID for the wall outlet to the active RF device based onthe wireless network protocol.
 3. The RFID system of claim 2 wherein:the aggregation further comprises the ID for the wall outlet.
 4. TheRFID system of claim 1 further comprising: the active RF device isfurther operable to transmit the aggregated information to a computerusing the wireless network protocol.
 5. The RFID system of claim 4further comprising: an application on the computer operable to processthe aggregated information to generate a log of the power usage for theelectrical device.
 6. The RFID system of claim 1 wherein: the wirelessnetwork protocol is based on the IEEE 802.15.4 standard.
 7. The RFIDsystem of claim 1 wherein: the wireless network protocol is based on theIEEE 802.11 standard.
 8. A method comprising: transmitting by an activeRadio Frequency (RF) device an RF signal based on a wireless networkprotocol; storing an identifier (ID) for an electrical device by a firstpassive RF device attached to a power cord of the electrical device,deriving, by the first passive RF device, power from the RF signal, andtransmitting, by the first passive RF device, the ID for the electricaldevice to the active RF device based on the wireless network protocol;storing an ID for a power strip by a second passive RF device attachedto a power strip that receives the power cord for the electrical device,deriving, by the second passive RF device, power from the RF signal, andtransmitting, by the second passive RF device, the ID for the powerstrip to the active RF device based on the wireless network protocol;and retrieving, by the active RF device, power usage data for theelectrical device from the power strip, and aggregating the ID for theelectrical device, the ID for the power strip, and the power usage datafor the electrical device.
 9. The method of claim 8 further comprising:storing an ID for the wall outlet by a third passive RF device attachedto a wall outlet that electrically connects to the power strip,deriving, by the third passive RF device, power from the RF signal, andtransmitting, by the third passive RF device, the ID for the wall outletto the active RF device based on the wireless network protocol.
 10. Themethod of claim 9 further comprising: including the ID for the walloutlet in the aggregation.
 11. The method of claim 8 further comprising:transmitting, with the active RF device, the aggregated information to acomputer using the wireless network protocol.
 12. The method of claim 11further comprising: processing, with an application on the computer, theaggregated information to generate a log of the power usage for theelectrical device.
 13. The method of claim 8 wherein: the wirelessnetwork protocol is based on the IEEE 802.15.4 standard.
 14. The methodof claim 8 wherein: the wireless network protocol is based on the IEEE802.11 standard.
 15. A Radio Frequency Identification (RFID) systemcomprising: an active RF device operable to generate a request, toencode the request based on a wireless network protocol, to modulate aradio frequency (RF) signal to include the encoded request, and totransmit the RF signal to a passive RF device.
 16. The RFID system ofclaim 15 wherein: the active RF device is operable to receive a responseto the request from the passive RF device, to generate anacknowledgement of the response, to encode the acknowledgement based onthe wireless network protocol, to modulate the RF signal to include theencoded acknowledgment, and to transmit the RF signal to the passive RFdevice.
 17. The RFID system of claim 15 wherein: the request indicates afile name; and the passive RF device is operable to identify a filestored in memory based on the file name in the request, and to insertthe file in a response.
 18. The RFID system of claim 15 wherein: thewireless network protocol is based on the IEEE 802.15.4 standard. 19.The RFID system of claim 15 wherein: the wireless network protocol isbased on the IEEE 802.11 standard.
 20. The RFID system of claim 15wherein: the request indicates a frequency for data transmittal.